CMOS and BICMOS are rapidly evolving as the premiere technology for integrating highly complex analog-digital subsystems on a single chip. Such single chip subsystems require precision capacitors. Polysilicon to polysilicon capacitors have been increasingly used to provide this necessary precision.
In prior art devices, several double level polysilicon (DLP) processes have often been developed to form the polysilicon to polysilicon capacitors. In particular, the LinEPIC DLP process uses a two-mask approach to define a capacitor bottom plate. The first polysilicon layer is masked and etched separate from the second polysilicon layer. Due to the separate masking and etching steps, this process has been considerably complicated and time consuming. Additionally, the topography that is associated with this DLP process requires an additional step of planarization prior to depositing metal on the appropriate contact points.
A second process known as the 4/3 Linear process uses a single mask approach to define a capacitor bottom plate. The first level of polysilicon serves as both the bottom plate and the CMOS gate. After the interlevel dielectric is formed, the second polysilicon layer is deposited to form the capacitor top plate. In order to eliminate filaments from the bottom plate edges and the CMOS gate edges, a large overetch is required. If there is a negative slope on the bottom plate edge, filaments will be trapped under the bottom plate edge. Since this is a DLP process, the added topography also requires additional planarization prior to metalization.
Therefore, a need has arisen for a simplified method of fabricating polysilicon to polysilicon capacitors used on CMOS and BICMOS. Additionally, it would be an advantageous to reduce the complications and expenses associated with DLP processes. There is also a need to eliminate filaments from the bottom plate edges and CMOS gate edges without requirement of a large overetch which may cause system failure. Finally, there is a need to eliminate the step of planarization prior to applying metal to the appropriate contacts.